A tryptophan derivative, ITE, enhances liver cell metabolic functions in vitro

Specific human CYP enzymes-dependent mutagenicity of tris(2-butoxyethyl) phosphate (an organophosphorus flame retardant) in human and hamster cell lines

Tris(2-butoxyethyl) phosphate (TBOEP) is an organophosphorus flame retardant ubiquitously present in the environment and even the human body. TBOEP is toxic in multiple tissues, which forms dealkylated and hydroxylated metabolites under incubation with human hepatic microsomes; however, the impact of TBOEP metabolism on its toxicity, particularly mutagenicity (typically requiring metabolic activation), is left unidentified. In this study, the mutagenicity of TBOEP in human hepatoma cell lines (HepG2 and C3A) and the role of specific CYPs were studied. Through molecular docking, TBOEP bound to human CYP1A1, 1B1, 2B6 and 3A4 with energies and conformations favorable for catalyzing reactions, while the conformations of its binding with human CYP1A2 and 2E1 appeared unfavorable. In C3A cells (endogenous CYPs being substantial), TBOEP exposing for 72 h (2-cell cycle) at low micromolar levels induced micronucleus, which was abolished by 1-aminobenzotriazole (inhibitor of CYPs); in HepG2 cells (CYPs being insufficient) TBOEP did not induce micronucleus, whose effect was however potentiated by pretreating the cells with PCB126 (CYP1A1 inducer) or rifampicin (CYP3A4 inducer). TBOEP induced micronucleus in Chinese hamster V79-derived cell lines genetically engineered for stably expressing human CYP1A1 and 3A4, but not in cells expressing the other CYPs. In C3A cells, TBOEP selectively induced centromere protein B-free micronucleus (visualized by immunofluorescence) and PIG-A gene mutations, and elevated γ-H2AX rather than p-H3 (by Western blot) which indicated specific double-strand DNA breaks. Therefore, this study suggests that TBOEP may induce DNA/chromosome breaks and gene mutations in human cells, which requires metabolic activation by CYPs, primarily CYP1A1 and 3A4.

A comprehensive review of advances in hepatocyte microencapsulation: selecting materials and preserving cell viability

Liver failure represents a critical medical condition with a traditionally grim prognosis, where treatment options have been notably limited. Historically, liver transplantation has stood as the sole definitive cure, yet the stark disparity between the limited availability of liver donations and the high demand for such organs has significantly hampered its feasibility. This discrepancy has necessitated the exploration of hepatocyte transplantation as a temporary, supportive intervention. In light of this, our review delves into the burgeoning field of hepatocyte transplantation, with a focus on the latest advancements in maintaining hepatocyte function, co-microencapsulation techniques, xenogeneic hepatocyte transplantation, and the selection of materials for microencapsulation. Our examination of hepatocyte microencapsulation research highlights that, to date, most studies have been conducted in vitro or using liver failure mouse models, with a notable paucity of experiments on larger mammals. The functionality of microencapsulated hepatocytes is primarily inferred through indirect measures such as urea and albumin production and the rate of ammonia clearance. Furthermore, research on the mechanisms underlying hepatocyte co-microencapsulation remains limited, and the practicality of xenogeneic hepatocyte transplantation requires further validation. The potential of hepatocyte microencapsulation extends beyond the current scope of application, suggesting a promising horizon for liver failure treatment modalities. Innovations in encapsulation materials and techniques aim to enhance cell viability and function, indicating a need for comprehensive studies that bridge the gap between small-scale laboratory success and clinical applicability. Moreover, the integration of bioengineering and regenerative medicine offers novel pathways to refine hepatocyte transplantation, potentially overcoming the challenges of immune rejection and ensuring the long-term functionality of transplanted cells. In conclusion, while hepatocyte microencapsulation and transplantation herald a new era in liver failure therapy, significant strides must be made to translate these experimental approaches into viable clinical solutions. Future research should aim to expand the experimental models to include larger mammals, thereby providing a clearer understanding of the clinical potential of these therapies. Additionally, a deeper exploration into the mechanisms of cell survival and function within microcapsules, alongside the development of innovative encapsulation materials, will be critical in advancing the field and offering new hope to patients with liver failure.

Induction of clastogenesis and gene mutations by carbamazepine (at its therapeutically effective serum levels) in mammalian cells and the dependence on human CYP2B6 enzyme activity

Carbamazepine (CBZ, an antiepileptic) is metabolized by multiple CYP enzymes to its epoxide and hydroxides; however, whether it is genotoxic remains unclear. In this study, molecular docking (CBZ to CYPs) and cytogenotoxic toxicity assays were employed to investigate the activation of CBZ for mutagenic effects, in various mammalian cell models. Docking results indicated that CBZ was valid as a substrate of human CYP2B6 and 2E1, while not for CYP1A1, 1A2, 1B1 or 3A4. In the Chinese hamster (V79) cell line and its derivatives genetically engineered for the expression of human CYP1A1, 1A2, 1B1, 2E1 or 3A4 CBZ (2.5 ~ 40 μM) did not induce micronucleus, while in human CYP2B6-expressing cells CBZ significantly induced micronucleus formation. In a human hepatoma C3A cell line, which endogenously expressed CYP2B6 twofold higher than in HepG2 cells, CBZ induced micronucleus potently, which was blocked by 1-aminobenzotriazole (inhibitor of CYPs) and ticlopidine (specific CYP2B6 inhibitor). In HepG2 cells CBZ did not induce micronucleus; however, pretreatment of the cells with CICTO (CYP2B6 inducer) led to micronucleus formation by CBZ, while rifampicin (CYP3A4 inducer) or PCB126 (CYP1A inducer) did not change the negative results. Immunofluorescent assay showed that CBZ selectively induced centromere-free micronucleus. Moreover, CBZ induced double-strand DNA breaks (γ-H2AX elevation, by Western blot) and PIG-A gene mutations (by flowcytometry) in C3A (threshold being 5 μM, lower than its therapeutic serum concentrations, 17 ~ 51 μM), with no effects in HepG2 cells. Clearly, CBZ may induce clastogenesis and gene mutations at its therapeutic concentrations, human CYP2B6 being a major activating enzyme.

Triphenyl phosphate induces clastogenic effects potently in mammalian cells, human CYP1A2 and 2E1 being major activating enzymes

As a new-type flame retardant and toxic substance, triphenyl phosphate (TPP) is a ubiquitous pollutant present even in human blood. TPP is transformed by human CYP enzymes to oxidized/dealkylated metabolites. The impact of TPP metabolism on its toxicity, however, remains unclear. In this study, the genotoxicity of TPP in several mammalian cell lines and its relevance to CYP/sulfortransferase (SULT) activities were investigated. The results indicated that TPP induced micronucleus formation at ≥1 μM concentrations in a human hepatoma (C3A, endogenous CYPs being substantial) cell line, which was abolished by 1-aminobenzotriazole (CYPs inhibitor). In cell line HepG2 (parental to C3A with lower CYP expression) TPP was inactive up to 10 μM, while pretreatment with ethanol (CYP2E1 inducer), PCB 126 (CYP1A inducer), or rifampicin (CYP3A inducer) led to micronucleus formation by TPP. In V79-Mz and V79-derived cells expressing human CYP1A1 TPP was inactive (up to 32 μM), and in cells expressing human CYP1B1, 2B6 and 3A4 it induced micronucleus weakly (positive only at 32 μM). However, TPP induced micronucleus potently in V79-derived cells expressing human CYP1A2, while this effect was drastically reduced by human SULT1A1 co-expression; likewise, TPP was inactive in cells expressing both human CYP2E1 and SULT1A1, but became positive with pentachlorophenol (inhibitor of SULT1) co-exposure. Moreover, in C3A cells TPP selectively induced centromere-free micronucleus (immunofluorescent assay), and TPP increased γ-H2AX (by Western blot, indicating double-strand DNA breaks). In conclusion, this study suggests that TPP is potently clastogenic, human CYP1A2 and 2E1 being major activating enzymes while SULT1A1 involved in detoxification.

Influence of aryl hydrocarbon receptor and sulfotransferase 1A1 on bisphenol AF-induced clastogenesis in human hepatoma cells

Bisphenol compounds (BPs) are ubiquitously existing pollutants. Recent evidence shows that they may be activated by human CYP1A1 for clastogenic effects; however, factors that influence/mediate CYP1A1-activated 4,4'-(hexafluoroisopropylidene)diphenol (BPAF) toxicity, particularly the aryl hydrocarbon receptor (AhR), sulfotransferase (SULT) 1A1 [known to conjugate 2,2-bis(4-hydroxyphenol)-propane (BPA)] and reactive oxygen species (ROS), remain unclear. In this study, a human hepatoma (HepG2) cell line was genetically engineered for the expression of human CYP1A1 and SULT1A1, producing HepG2-hCYP1A1 and HepG2-hSULT1A1, respectively. They were used in the micronucleus test and γ-H2AX analysis (Western blot) (indicating double-strand DNA breaks) with BPAF; the role of AhR in mediating BPAF toxicity was investigated by coexposure of AhR modulators in HepG2 and its derivative C3A (with no genetic modifications but enhanced CYP expression). The results indicated induction of micronuclei by BPAF (≥ 2.5 µM, for 2-cell cycle) in HepG2-hCYP1A1 and C3A, while inactive in HepG2 and HepG2-hSULT1A1; however, BPAF induced micronuclei in HepG2 pretreated with 3,3',4,4',5-pentachlorobiphenyl (PCB126, AhR activator), and BAY-218 (AhR inhibitor) blocked the effect of BPAF in C3A. In HepG2-hCYP1A1 BPAF selectively induced centromere-free micronuclei (immunofluorescent assay) and double-strand DNA breaks. In HepG2 cells receiving conditional medium from BPAF-HepG2-hCYP1A1 incubation micronuclei were formed, while negative in HepG2-hSULT1A1. Finally, the intracellular levels of ROS, superoxide dismutase and reduced glutathione in C3A and HepG2-hCYP1A1 exposed to BPAF were all moderately increased, while unchanged in HepG2 cells. In conclusion, like other BPs BPAF is activated by human CYP1A1 for potent clastogenicity, and this effect is enhanced by AhR while alleviated by SULT1A1.

Effects of Tyrosine and Tryptophan in Rats with Diet-Induced Obesity

Amino acids tyrosine (Tyr) and tryptophan (Trp) play a significant role in the regulation of energy metabolism, locomotor activity, and eating behavior. We studied the possibility of modulating these processes in obesity by increasing the pool of Tyr and Trp in the experimental diet. As a model of obesity, we used Wistar rats fed a diet with an excess specific energy value (HFCD) for 64 days. Trp led to a normalization of the rats’ body weight almost to the control level, but increased anxiety-like behavior and decreased long-term memory. The consumption of amino acids resulted in increased grip strength and impairment of short-term memory. The locomotor activity of animals decreased with age as a result of Tyr consumption, while Trp, on the contrary, prevented this. The Tyr supplementation led to the normalization of triglycerides and LDL. In the spleen cell lysates, amino acids suppressed the production of proinflammatory cytokines. The liver tissue morphology showed that the consumption of Tyr noticeably weakened the signs of fatty degeneration. The addition of Trp, on the contrary, led to an unfavorable effect, consisting of the appearance of a high number of large rounded fatty vacuoles. The data obtained indicate a more pronounced anti-inflammatory effect of Tyr as compared to Trp.

Potent Clastogenicity of Bisphenol Compounds in Mammalian Cells-Human CYP1A1 Being a Major Activating Enzyme

Bisphenols (BPs) are environmental pollutants with relevant DNA damage in human population; however, they are generally inactive in standard mutagenicity assays, possibly due to insufficient metabolic activation. In this study, induction of micronuclei and double-strand DNA breaks by BPA, BPF, and BPS in Chinese hamster V79-derived cell lines expressing various human CYP enzymes and a human hepatoma (C3A) (metabolism-proficient) cell line were investigated. Molecular docking of BPs to human CYPs indicated some substrate-enzyme potentials, including CYP1A1 for each compound, which did not induce micronuclei in V79-derived cell lines expressing human CYP1A2, 2E1, or 3A4 but became positive in human CYP1A1-expressing (V79-hCYP1A1) cells. In V79-hCYP1A1 and C3A cells, all compounds induced double-strand DNA breaks and micronuclei formation, which were blocked/significantly attenuated by 1-aminobenzotriazole (CYP inhibitor) or 7-hydroxyflavone (selective CYP1A1 inhibitor). Coexposure of C3A cells to pentachlorophenol (sulfotransferase 1 inhibitor) or ketoconazole (UDP-glucuronosyltransferase 1A inhibitor) potentiated micronuclei induction by each compound, with thresholds lowered from 2.5-5.0 to 0.6-1.2 μM. Immunofluorescence staining of centromere protein B with micronuclei formed in C3A cells by each compound indicated pure clastogenic effects. In conclusion, BPs are potently clastogenic in mammalian cells, which require activation primarily by human CYP1A1 and are negatively modulated by phase II metabolism.

Potent aneugenicity of 1-methylpyrene in human cells dependent on metabolic activation by endogenous enzymes

1-Methylpyrene (1-MP) is a common environmental pollutant and animal carcinogen. After sequential activation by cytochromes P450 and sulfotransferases, it induced gene mutations and micronuclei in mammalian cells. The type of micronuclei formed, entire chromosomes or fragments, was not analysed. In this study, 1-MP and its primary metabolite, 1-hydroxymethylpyrene (1-HMP), were investigated for the induction of centromere-positive and -negative micronuclei in the human hepatoma cell line HepG2 and its derivative C3A, expressing relevant enzymes at higher levels. Under a short-exposure (9 h)/long-recovery regime (2 cell cycles in total), 1-MP and 1-HMP provided negative test results in HepG2 cells. However, they induced micronuclei in C3A cells, the effect being blocked by 1-aminobenzotriazole (inhibitor of cytochromes P450s) and reduced by pentachlorophenol (inhibitor of sulfotransferases). Immunofluorescence staining of centromere protein B in the micronuclei revealed purely clastogenic effects under this regime. Unexpectedly, 1-MP and 1-HMP at concentrations 1/5-1/4 of that required for micronuclei formation led to mitotic arrest and spindle aberrations, as detected by immunofluorescence staining of β- and γ-tubulin. Following extended exposure (72 h, 2 cell cycles, no recovery), damage to the spindle apparatus and centrosomes was detected at even lower concentrations, with concurrent formation of micronuclei. At low concentrations (1-8 µM 1-MP, 0.25-0.5 µM 1-HMP), the micronuclei induced were unexceptionally centromere-positive. Thus, the chromosome-damaging mechanism of 1-MP was regime and concentration dependent: potently aneugenic under persistent exposure, while clastogenic at higher concentrations following a short-exposure/long-recovery regime. This is a convincing evidence for the existence of metabolic activation-dependent aneugens.

Bioengineering Organs for Blood Detoxification

For patients with severe kidney or liver failure the best solution is currently organ transplantation. However, not all patients are eligible for transplantation and due to limited organ availability, most patients are currently treated with therapies using artificial kidney and artificial liver devices. These therapies, despite their relative success in preserving the patients' life, have important limitations since they can only replace part of the natural kidney or liver functions. As blood detoxification (and other functions) in these highly perfused organs is achieved by specialized cells, it seems relevant to review the approaches leading to bioengineered organs fulfilling most of the native organ functions. There, the culture of cells of specific phenotypes on adapted scaffolds that can be perfused takes place. In this review paper, first the functions of kidney and liver organs are briefly described. Then artificial kidney/liver devices, bioartificial kidney devices, and bioartificial liver devices are focused on, as well as biohybrid constructs obtained by decellularization and recellularization of animal organs. For all organs, a thorough overview of the literature is given and the perspectives for their application in the clinic are discussed.

Current High-Throughput Approaches of Screening Modulatory Effects of Xenobiotics on Cytochrome P450 (CYP) Enzymes

Cytochrome P450 (CYP) is a critical drug-metabolizing enzyme superfamily. Modulation of CYP enzyme activities has the potential to cause drug–drug/herb interactions. Drug–drug/herb interactions can lead to serious adverse drug reactions (ADRs) or drug failures. Therefore, there is a need to examine the modulatory effects of new drug entities or herbal preparations on a wide range of CYP isoforms. The classic method of quantifying CYP enzyme activities is based on high-performance liquid chromatography (HPLC), which is time- and reagent-consuming. In the past two decades, high-throughput screening methods including fluorescence-based, luminescence-based, and mass-spectrometry-based assays have been developed and widely applied to estimate CYP enzyme activities. In general, these methods are faster and use lower volume of reagents than HPLC. However, each high-throughput method has its own limitations. Investigators may make a selection of these methods based on the available equipment in the laboratory, budget, and enzyme sources supplied. Furthermore, the current high-throughput systems should look into developing a reliable automation mechanism to accomplish ultra-high-throughput screening in the near future.

Aryl hydrocarbon receptor (AHR): "pioneer member" of the basic-helix/loop/helix per-Arnt-sim (bHLH/PAS) family of "sensors" of foreign and endogenous signals

The basic-helix/loop/helix per-Arnt-sim (bHLH/PAS) family comprises many transcription factors, found throughout all three kingdoms of life; bHLH/PAS members "sense" innumerable intracellular and extracellular "signals" - including endogenous compounds, foreign chemicals, gas molecules, redox potential, photons (light), gravity, heat, and osmotic pressure. These signals then initiate downstream signaling pathways involved in responding to that signal. The term "PAS", abbreviation for "per-Arnt-sim" was first coined in 1991. Although the mouse Arnt gene was not identified until 1991, evidence of its co-transcriptional binding partner, aryl hydrocarbon receptor (AHR), was first reported in 1974 as a "sensor" of foreign chemicals, up-regulating cytochrome P450 family 1 (CYP1) and other enzyme activities that usually metabolize the signaling chemical. Within a few years, AHR was proposed also to participate in inflammation. The mouse [Ah] locus was shown (1973-1989) to be relevant to chemical carcinogenesis, mutagenesis, toxicity and teratogenesis, the mouse Ahr gene was cloned in 1992, and the first Ahr(-/-) knockout mouse line was reported in 1995. After thousands of studies from the early 1970s to present day, we now realize that AHR participates in dozens of signaling pathways involved in critical-life processes, affecting virtually every organ and cell-type in the animal, including many invertebrates.